Typically, cancer radiation therapy lasts more than a month, and unplanned treatment interruptions occur for about half of all patients. Tumors and surrounding normal tissues are affected differently by such interruptions, due to differences in growth rates and in cellular repair capabilities. Consequently, optimally compensating for interruptions requires estimates based on cellular radiobiology. Currently accepted state-of-the-art techniques in radiobiology will be used as a basis for designing and writing readily usable software, for a personal computer or a Macintosh, which makes available to the radiation oncologist a variety of compensation options for unplanned interruptions. The software will also indicate possible drawbacks of each option. The programs will be simple enough that at least one professional at each radiation oncology facility will be able to use them interactively, with a thorough understanding of their implications. Preliminary studies on the feasibility of integrating radiobiological concepts into full-scale treatment-planning computer codes will also be carried out.